The present invention relates generally to photonic switches, and more particularly to a method for isolating faults in interconnections between photonic switches.
Optical fibers are increasingly prevalent in the transmission lines of data networks, due to their higher bandwidth capabilities compared to wire transmission lines. Before the photonic switch was invented, light signals switching from one optical fiber to another first were converted to and from electrical impulses using optical-to-electrical-to-optical equipment. The conversion process was time-consuming and slowed the speed of data traveling in the network. The photonic switch provided a way to keep the data network completely optical and thus speed up data transfer rates.
Many photonic switches are designed to be modular, so that several photonic switches can be connected together using optical fibers to create one larger photonic switch, hereinafter called a photonic switch network. The modularity of the photonic switches gives the customer the flexibility to make a photonic switch network as large or small as desired. The optical fibers in a photonic switch network have to be tested for continuity and proper operation. Typically, an optical fiber is tested by transmitting light through one end of the optical fiber, and checking for the light at the other end with a detector. When the light is detected, the optical fiber is working correctly. When no light is detected, a break in continuityxe2x80x94also known as a faultxe2x80x94exists within the optical fiber, and the optical fiber must either be fixed or replaced.
In the past, testing the continuity of the interconnecting optical fibers in a photonic switch network was not a simple matter. The optical fibers are connected directly from the data output of one switch to the data input of another, making it difficult to access any of the test light signals. One prior art solution was to use an optical fiber with a light-dividing device, such as a tap or splinter, for each interconnection between photonic switches. A tap or spliter is an optical d device that splits the original signal into two or more signals. These split-off signals may or may not differ from each other in signal strength, but are identical in data content. One of the split signals would lead to the normal data path, maintaining the data connection; another signal can be drawn off into a test system. There are drawbacks to this method. First, an optical fiber with a light-dividing device is more expensive than a plain optical fiber. When there are thousands of interconnections to be tested, the additional cost of the light-dividing devices can be quite high. Secondly, the light-dividing device itself can introduce faults into the photonic switch network. This makes it difficult to determine whether a fault lies in an optical fiber, or the associated light-dividing device. Finally, the power of each split-off signal is less than the original, which can cause problems during testing. If the split-off test signal from an optical fiber is too weak, the detector will be unable to detect it, and would instead indicate a fault in that particular optical fiber where none exists. This mistake can cause a flawless optical fiber to be needlessly replaced.
Accordingly, there remains a need for an improved method for testing interconnecting optical fibers in a photonic switch network.
The present invention provides a simple and reliable method for isolating faults in interconnections between photonic switches. The photonic switches are first verified individually, using self-test paths built into every photonic switch. Once each individual photonic switch has been verified, the interconnecting optical fibers of the photonic switch network are checked. Each photonic switch is equipped with a transceiver consisting of a transmitter and a receiver. During test, a photonic switch uses its transmitter to transmit light through an optical fiber interconnection to a second photonic switch. Pre-existing pathways within the photonic switches are used to access and route the test light signals, thus eliminating the need for light-dividing devices altogether. When the second photonic switch detects the transmitted light with its receiver, the optical fiber interconnection passes the continuity test. When the second photonic switch cannot detect the light, the optical fiber interconnection has a fault that must be repaired. By repeating this process for all optical fiber interconnections between all photonic switches, the photonic switch network can be tested for proper operation.
Further features of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying exemplary drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.